Bone graft substitute composition

ABSTRACT

Bone graft substitute compositions and methods of making the compositions are disclosed. In some embodiments, a method of making a composition includes contacting a mixing solution with a first mixture having calcium sulfate hemihydrate and a plasticizing material to form a second mixture; waiting a predetermined period of time after forming said second mixture; and then contacting demineralized bone with the second mixture to form the composition. A composition can be formed from a kit including a first mixture having calcium sulfate hemihydrate and a plasticizing substance, a second mixture having demineralized bone, and a mixing solution. The first and second mixtures and the mixing solution are unblended.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 10/448,885, filed May 30, 2003, which is a continuation-in-partapplication of U.S. application Ser. No. 10/179,533, filed Jun. 24,2002, which are hereby incorporated herein in their entirety byreference.

TECHNICAL FIELD

The invention relates to bone graft substitute compositions.

BACKGROUND OF THE INVENTION

Compositions containing calcium sulfate can be used as filler for voidsand/or defects defined by bone. In some embodiments, the compositionscan promote bone growth.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the invention relates to bone graft substitutecompositions.

In another aspect, the invention features a method of making acomposition. The method includes contacting a mixing solution with afirst mixture having calcium sulfate hemihydrate and a plasticizingmaterial to form a second mixture; and after waiting a predeterminedtime, contacting demineralized bone with the second mixture to form thecomposition.

In another aspect, the invention features a kit, including a firstmixture having calcium sulfate hemihydrate and a plasticizing substance,a second mixture having demineralized bone, the second mixture beingunblended with the first mixture, and a mixing solution unblended withthe first and second mixtures. The kit can include instructions formaking a bone graft composition as described herein.

The first mixture can further include a first material capable ofaccelerating formation of calcium sulfate dihydrate from the calciumsulfate hemihydrate, such as calcium sulfate dihydrate coated withsucrose.

Other aspects, features, and advantages of the invention will beapparent from the description of the preferred embodiments thereof andfrom the claims.

DETAILED DESCRIPTION OF THE INVENTION

Bone graft substitute compositions including surgical-grade calciumsulfate hemihydrate (CaSO₄.½H₂O); demineralized bone matrix; a materialthat accelerates hardening of the composition (“an accelerant”); aplasticizing material; and a mixing solution are described inApplicants' co-pending U.S. Ser. No. 10/179,533. Furthermore, bone graftcompositions including surgical-grade calcium sulfate hemihydrate(CaSO₄.½H₂O); demineralized bone matrix; a plasticizing material; and amixing solution are also described in Applicants'0 co-pending U.S. Ser.No. 10/060,697 (and other members of that family). These compositionsare prepared by mixing all the dry materials together simultaneously,and then combining the dry materials with the mixing solution.

Here, Applicants have found that during use, if the components are mixedtogether in a predetermined order and timing, consistent results, suchas repeatable set times, are much likely to be obtained. Applicants havefound that the order and timing to be to first form a first mixtureincluding the calcium sulfate, the plasticizing material, and theoptional accelerant in a container. The mixing solution is then added tothe container. The first mixture and the solution are mixed untilblended, e.g., for about thirty seconds, and allowed to sit, e.g., forabout another thirty seconds. During the initial one minute, the blendof the first mixture and mixing solution can be mixed the entire time oronly a portion of the time (e.g., mixing and sitting).

After a total of about one minute, the demineralized bone is then addedto the blend and mixed thoroughly to form the composition. Thecomposition can be delivered to a target site (e.g., a void or a defect)by injecting the composition through a syringe, and/or by forming (e.g.,molding) a paste or a putty of the composition and applying thecomposition by hand (e.g., using fingers). After about 5-10 minutes, thecomposition can harden ex vivo or in vivo, e.g., to a hardnesssufficient to support orthopedic hardware.

Without wishing to be bound by theory, it is believed that during use,e.g., after mixing the mixture of powders with the mixing solution, thecalcium sulfate hemihydrate is converted, e.g., changes crystallineform, into calcium sulfate dihydrate (CaSO₄.2H₂O), which hardens thecomposition. Calcium sulfate dihydrate is capable of being sorbed by thebody. It is believed that the method described above of making thecomposition allows the calcium sulfate hemihydrate to begin convertingto calcium sulfate dihydrate before other ingredients of thecomposition, such as proteins from the demineralized bone, interfere(e.g., stop) the conversion. In any event, beneficial results have beenfound by waiting a predetermined period of time before adding thedemineralized bone to the second mixture. This method is different from,for example, U.S. Pat. No. 5,385,887, to Yim, in which calcium sulfateis added directly to a blood-BMP mixture.

For purposes of describing the concentrations of materials in the bonegraft substitute composition, the composition includes 100 parts ofcalcium sulfate, e.g., calcium sulfate hemihydrate. Methods of making acalcium sulfate hemihydrate are described in U.S. Pat. Nos. 5,614,206,5,807,567, and 6,030,636, each of which is hereby incorporated byreference in its entirety.

The demineralized bone matrix is believed to enhance bone growth. Insome embodiments, the demineralized bone matrix is freeze-dried to lessthan about 6% moisture. The demineralized bone matrix can have aparticle size of about 125-850 microns, e.g., about 125-710 microns. Theparticle size can be greater than or equal to about 125, 150, 200, 250,300, 350, 400, 450, 500, 550, 600, 650, 700, 750, or 800 microns; and/orless than or equal to about 850, 800, 750, 700, 650, 600, 550, 500, 450,400, 350, 300, 250, 200, or 150 microns. The calcium content in thedemineralized bone matrix can be about less than eight (8) percent.Demineralized bone matrix is available, e.g., from Allosource (Denver,Colo.) or DCI (Nashville, Tenn.).

For 100 parts of calcium sulfate (e.g., CaSO₄.½H₂O), the compositionincludes between about 10 and about 30 parts of demineralized bonematrix, such as between about 15 and about 25 parts, or between about 19and about 21 parts, or about 20 parts. In embodiments, the compositionmay include greater than or equal to about 10, 12, 14, 16, 18, 20, 22,24, 26, or 28 parts of demineralized bone matrix; and/or less than orequal to about 30, 28, 26, 24, 22, 20, 18, 16, 14, or 12 parts ofdemineralized bone matrix.

As described in Applicants' co-pending U.S. Ser. No. 10/179,533 andwithout wishing to be bound by theory, the accelerant is believed toenhance, e.g., accelerate, the conversion of calcium sulfate hemihydrateto calcium sulfate dihydrate. In particular, it is believed thatparticles of the accelerant act as crystallization nucleation sites forthe conversion of calcium sulfate hemihydrate to calcium sulfatedihydrate. Examples of accelerants include calcium sulfate dihydrate,potassium sulfate, or sodium sulfate. Other examples include ionicsalts. A preferred accelerant is calcium sulfate dihydrate crystals(available from U.S. Gypsum) coated with sucrose (available from VWRScientific Products). A process of stabilizing the dihydrate crystals bycoating with sucrose is described in U.S. Pat. No. 3,573,947, herebyincorporated by reference in its entirety.

For 100 parts of calcium sulfate (e.g., CaSO₄.½H₂O), the compositionincludes between about 0.5 and about 5 parts of the accelerant, such asabout 4.8 parts, or between about 1 and about 4 parts, or between about2.5 and about 3.5 parts, or about 3 parts. The composition may includegreater than or equal to about 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, or 4.5parts of the accelerant; and/or less than or equal to about 5, 4.5, 4,3.5, 3, 2.5, 2, 1.5, or 1 parts of the accelerant. Mixtures of two ormore accelerants can be used.

The plasticizing material is believed to provide the bone graftsubstitute composition with a consistency that helps the composition toform into a paste or putty, or to flow, e.g., to be injectable. Examplesof plasticizing materials include cellulose derivatives, such as sodiumcarboxymethylcellulose, methylcellulose (MC),hydroxypropylmethylcellulose (HPMC), hydroxypropylcellulose (HPC),ethylcellulose (EC), hydroxyethylcellulose or cellulose acetatebutyrate. Other examples of plasticizing material include high molecularweight alcohols including glycerol and vinyl alcohols, stearic acid, andhyaluronic acid.

For 100 parts of calcium sulfate (e.g., CaSO₄.½H₂O), the compositionincludes between about 0.5 and about 5 parts of the plasticizingmaterial, such as between about 1 and about 3 parts, or between about1.5 and about 2.5 parts, or about 2 parts. The composition may includegreater than or equal to about 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, or 4.5parts of the plasticizing material; and/or less than or equal to about5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, or 1 parts of the plasticizing material.Mixtures of two or more plasticizing materials can be used.

The mixing solution is generally selected to provide the compositionwith a desired consistency and hardening time. Examples of a mixingsolution include water, e.g., sterile water, solutions containinginorganic salts, or cationic surface active agents including sodiumchloride, saline, e.g., phosphate buffered saline, potassium chloride,sodium sulfate, potassium sulfate, EDTA, ammonium sulfate, ammoniumacetate, and sodium acetate. A specific example of a mixing solution is0.9% NaCl saline solution (available from Baxter).

The concentration of mixing solution in the substitute compositionvaries and can be a function of, for example, the source (e.g., tissuebank) of the demineralized bone matrix, and/or the desired consistencyof the composition. Also, the amount of mixing solution added to themixture of powders can affect the time the composition takes to set,i.e., the set time. Increasing the amount of mixing solution canincrease the set time, and decreasing the amount of mixing solutionadded to the mixture of powders can reduce the set time. For example,for a putty having HPMC, 2.6 grams of water provided a set time of about10-15 minutes, while 4.0 grams of water provided a set time of about 60minutes.

In some embodiments, for 100 parts of calcium sulfate (e.g.,CaSO₄.½H₂O), the composition includes between about 40 and about 60parts of the mixing solution, such as between about 45 and about 55parts, or between about 49 and about 51 parts, or about 50 parts. Thecomposition may include greater than or equal to about 40, 45, 50, or 55parts of the mixing solution; and/or less than or equal to about 60, 55,50, or 45 parts of the mixing solution. Mixtures of two or more mixingsolutions can be used.

The mixing solution can further include one or more additives such as,for example, bone marrow aspirate, platelet concentrate, blood,pharmaceutical additives in solution, or combinations of thesematerials. Other examples of additives include medicaments orpesticides. Examples of medicaments are antibiotics, chemotherapeuticagents, growth factors, and analgesics. Examples of antibiotics aretetracycline hydrochloride, vancomycin, cephalosporins, andaminoglycocides such as tobramycin and gentamicin. Examples ofchemotherapeutic agents are cis-platinum, ifosfamide, methotrexate, anddoxorubicin hydrochloride (Adriamycin®). Examples of growth factors aretransforming growth factor beta (TGF-Beta), bone morphogenic protein(BMP), basic fibroblast growth factor, platelet-derived growth factor,and other polypeptide growth factors. Examples of analgesics areanesthetics such as lidocaine hydrochloride (Xylocaine®), bipivacainehydrochloride (Marcaine®), and non-steroidal anti-inflammatory drugssuch as ketorolac tromethamine (Toradol®) Certain mixing solution and/oradditives can affect, e.g., delay, the hardening properties of thecomposition. The additive(s) can be added to the composition after thedemineralized bone matrix has been added.

The composition as formed can be a conforming material having apaste-like or putty-like consistency, e.g., like Plaster of Paris, thatcan be applied digitally. The composition can be injected into a targetsite, for example, to fill into cracks or voids. In some embodiments,the composition is capable of setting to a hardness, e.g., about 4.3MPa, in about 5-15 minutes, e.g., greater than 5, 7, 9, 11, or 13minutes, and/or less than 15, 13, 11, 9, or 7 minutes.

The hardened composition can be used for intra-operative support ofhardware, such as orthopedic hardware, e.g., bone plates, distal radiushardware, and hardware used for tibial plateau fractures.

The following example is illustrative and not intended to be limiting.

EXAMPLE

A mixture of surgical-grade calcium sulfate hemihydrate (SGCSH) andhydroxypropylmethylcellulose (5.0 g total, 4.9 g hemihydrate with 0.1 gHPMC) was mixed and bottled. In a separate bottle, 0.96 g DBM waspackaged. In a third vial, 2.38 g water was packaged. All three bottleswere electron beam sterilized at 18-26 kGy. To mix the putty, the SGCSHblend was emptied into a bowl and the water was added. The powder wasmixed for approximately 30 seconds and then allowed to rest for 30seconds. After one minute had passed since the water had been added tothe hemihydrate powder, the DBM was added to the calcium sulfate mixtureand mixed thoroughly for approximately 30 seconds. A putty like materialwas formed, setting in approximately 7 minutes. The strength of thehardened putty was approximately 4 MPa.

Other Embodiments

In some embodiments, the composition further includes a bioactive agent.Examples of bioactive agents include growth factors, hyaluronic acid,bone morphogenic proteins, bone autograft, and bone marrow, etc. Thecomposition may include sodium bicarbonate. For example, the compositionmay include 0.1-2% sodium bicarbonate by weight to provide a porousstructure in the resultant composition.

Alternatively or in addition, the bone graft substitute composition mayinclude one or more additives such as an antiviral agent, anantimicrobial agent, an antibiotic agent, an amino acid, a peptide, avitamin, an inorganic element, a protein synthesis co-factor, a hormone,an endocrine tissue, a synthesizer, an enzyme, a polymer cellscaffolding agent with parenchymal cells, an angiogenic drug, a collagenlattice, an antigenic agent, a cytoskeletal agent, mesenchymal stemcells, a bone digester, an antitumor agent, an cellular attractant,fibronectin, a growth hormone, a cellular attachment agent, animmunosuppressant, a nucleic acid, a surface active agent, syntheticallyderived or naturally derived chips of minerals such as calciumphosphate, e.g., hydroxyapatite or tricalcium phosphate, or calciumcarbonate, a penetration enhancer, allografts, e.g., a bone allograft,cancellous bone chip (an osteoconductive substrate), and chunks, shards,and/or pellets of calcium sulfate.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.

1. A method of making a bone graft substitute composition, comprising:mixing calcium sulfate hemihydrate, a plasticizing material, and anaqueous mixing solution for a time sufficient to form a blend; waiting apredetermined period of time after forming the blend, wherein saidpredetermined period of time is at least about thirty seconds after theblend is formed; and forming a mixture of the blend and a demineralizedbone material following the predetermined period of time to produce thebone graft substitute composition.
 2. The method of claim 1, wherein theblend is continuously mixed during the predetermined period of time. 3.The method of claim 1, wherein said mixing step comprises mixing for atleast about 30 seconds to form the blend.
 4. The method of claim 1,wherein the time utilized to form the blend and the predetermined periodof time equal at least about one minute.
 5. The method of claim 1,wherein the blend further comprises an accelerant that acceleratesformation of calcium sulfate dihydrate from the calcium sulfatehemihydrate.
 6. The method of claim 5, wherein the accelerant isselected from the group consisting of calcium sulfate dihydrate,potassium sulfate, sodium sulfate, and mixtures thereof.
 7. The methodof claim 5, wherein the accelerant is calcium sulfate dihydrate coatedwith sucrose.
 8. The method of claim 1, wherein the plasticizingmaterial is selected from the group consisting of cellulose derivatives,glycerol, vinyl alcohols, stearic acid, hyaluronic acid, and mixturesthereof.
 9. The method of claim 1, wherein the plasticizing material isselected from the group consisting of sodium carboxymethylcellulose,methylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose,ethylcellulose, hydroxyethylcellulose, cellulose acetate butyrate, andmixtures thereof.
 10. The method of claim 1, wherein the aqueous mixingsolution comprises sterile water, the water optionally comprisinginorganic salts or cationic surface active agents.
 11. The method ofclaim 1, further comprising mixing an additive into the blend or themixture of the blend and the demineralized bone material, the additivebeing selected from the group consisting of bone marrow aspirate,platelet concentrate, blood, medicaments, pesticides, sodiumbicarbonate, growth factors, bone morphogenic proteins, bone autograft,calcium phosphates, calcium carbonate, and mixtures thereof.
 12. Themethod of claim 1, wherein the bone graft substitute composition has theconsistency of a paste or putty, and can be applied to the site of abone defect digitally or by injection.
 13. The method of claim 1,wherein the demineralized bone material is in freeze-dried form and hasa particle size of about 125 to about 850 microns.
 14. The method ofclaim 1, wherein the bone graft substitute composition comprises: 100parts of calcium sulfate hemihydrate; about 0.5 to about 5 parts of theplasticizing material; and about 10 to about 30 parts of demineralizedbone.
 15. The method of claim 1, wherein the bone graft substitutecomposition comprises: 100 parts of calcium sulfate hemihydrate; about0.5 to about 5 parts of an accelerant that accelerates formation ofcalcium sulfate dihydrate from the calcium sulfate hemihydrate; about0.5 to about 5 parts of a plasticizing material; and about 10 to about30 parts of demineralized bone.
 16. A bone graft substitute compositionmade by a method according to claim
 1. 17. A kit for forming a bonegraft substitute composition, comprising: a dry powder mixture ofcalcium sulfate hemihydrate and a plasticizing material; an aqueousmixing solution; a demineralized bone material in particulate formunblended with the dry powder mixture or the aqueous mixing solution;and a set of instructions directing a kit user to perform the method ofclaim
 1. 18. A method of making a bone graft substitute composition,comprising: mixing surgical grade calcium sulfate hemihydrate, acellulose derivative, calcium sulfate dihydrate coated with sucrose, andan aqueous mixing solution for a time sufficient to form a blend;waiting a predetermined period of time after forming the blend, whereinsaid predetermined period of time is at least about thirty seconds afterthe blend is formed; and forming a mixture of the blend and afreeze-dried demineralized bone material following the predeterminedperiod of time to produce the bone graft substitute composition, whereinthe bone graft substitute composition has the consistency of a paste orputty, and can be applied to the site of a bone defect digitally or byinjection.
 19. The method of claim 18, wherein the time utilized to formthe blend and the predetermined period of time equal at least about oneminute.
 20. A kit for forming a bone graft substitute composition,comprising: a dry powder mixture of calcium sulfate hemihydrate and aplasticizing material; an aqueous mixing solution; and a demineralizedbone material in particulate form unblended with the dry powder mixtureor the aqueous mixing solution.
 21. The kit of claim 20, wherein the drypowder mixture further comprises an accelerant that acceleratesformation of calcium sulfate dihydrate from the calcium sulfatehemihydrate.
 21. The kit of claim 21, wherein the accelerant is calciumsulfate dihydrate coated with sucrose.
 23. The kit of claim 20, whereinthe plasticizing material is selected from the group consisting ofcellulose derivatives, glycerol, vinyl alcohols, stearic acid,hyaluronic acid, and mixtures thereof.
 24. The kit of claim 20, whereinthe plasticizing material is selected from the group consisting ofsodium carboxymethylcellulose, methylcellulose,hydroxypropylmethylcellulose, hydroxypropylcellulose, ethylcellulose,hydroxyethylcellulose, cellulose acetate butyrate, and mixtures thereof.25. The kit of claim 20, wherein the demineralized bone material is infreeze-dried form and has a particle size of about 125 to about 850microns.